The present invention relates generally to washing machines, and more particularly pertains to the control of a washing machine which employs a variable speed electronically commutated motor (ECM) coupled to an agitator and a basket.
Conventional washing machines typically include a basket that holds articles such as clothes to be washed, an agitator disposed within the basket which agitates the clothes in the basket during a wash cycle, and a motor which drives the agitator and the basket. The motor is typically an AC induction motor, which can reverse its rotation direction to achieve different modes of operation during a wash cycle. The motor, for example, may rotate in a first direction during an agitation mode and a second direction, opposite the first direction, in a spin mode.
In a conventional washing machine, a transmission is typically provided, and it comprises gears, a concentric lobe and follower, and rack and pinion components to convert a rotational motion of the AC induction motor into an oscillatory motion of the agitator during an agitation mode. Additional mechanisms are provided to bypass the transmission to obtain high speed rotation during the spin mode. In addition, a brake is typically associated with the transmission to hold the transmission (and hence the basket) immobile during an agitation mode, and a clutch or actuator is provided to engage or disengage the brake. Further, an additional slip clutch is typically installed between the motor and the agitator, since the AC induction motor cannot immediately generate the required full torque.
Although washing machines powered by AC induction motors generally operate in a satisfactory manner, they are generally both complicated and inflexible. For example, the transmission is a relatively complex unit that includes many moving parts and contributes substantially to the unreliability and cost of the washing machine. It is also configured to provide only a limited number of options with regard to the motions of the basket and the agitator.
To overcome some of the limitations of conventional AC induction motor powered washing machines, variable speed reversible electric motors have been implemented to simplify the construction of washing machines and to allow more flexibility in controlling the motions of the basket and the agitator.
The rotational speed and direction of a variable speed reversible electric motor, sometimes referred to as an electronically commutated motor (ECM), can be controlled with electronic commutation equipment which enables the ECM to move in a clockwise or counterclockwise motion causing the agitator to oscillate clockwise or counterclockwise in an agitation mode. Although washing machines employing an ECM have certain advantages over prior art AC induction motor powered washing machines, problems remain with simplifying the precise control of the ECM during agitation, due to variations in the load size of clothing and other articles to be washed.
The present invention provides a washing machine with the flexibility of a variable speed reversible electric motor that has a simplified control capable of precisely controlling various agitation cycles under differing load conditions. The washing machine comprises an agitator for agitating articles of clothing and the like to be washed and an agitator drive shaft connected to the agitator for driving the agitator. A variable speed electronically commutated motor (ECM) is provided for driving the agitator drive shaft and a basket drive shaft which drives the basket of the washing machine. The agitator drive shaft may be directly connected to the rotor of the ECM or connected to the rotor of the ECM by a belt between an ECM pulley and an agitator pulley, or through a simple gear reducer.
When driving the agitator drive shaft, an ECM control unit provides current commands to the ECM to produce a variety of agitation cycles. The current commands produced by the ECM control unit are generated by a microprocessor which implements a feedback control system that compares a digitally generated sinewave agitator position command, stored in a read-only-memory (ROM) and selected by the user to implement a specific agitation cycle, with a measured agitator position. Measurement of the agitator position, and the direction of motion of the agitator at any time during an agitator cycle, are provided by processing the signals of three adjacent Hall sensors positioned near the rotor of the ECM. The three Hall sensors provide basic rotor position information used to direct the gating action of power transistors in the controller. The Hall sensors can only indicate six unique localized position sectors that are repeated many times over a rotor motion providing typical washer agitation motion.
Since the ECM rotor can only rotate from one sector to another sector at any given time, the ECM control unit can determine whether the rotor, and thus the agitator, is moving clockwise, counterclockwise or reversing its rotation by processing the sector indications produced by the three Hall sensors. This information is used to construct a facsimile of the agitator position, referred to here as the constructed agitator position. Using a standard feedback control loop which compares the measured agitator position with the sinewave position command, the microprocessor of the ECM control unit outputs an ECM current command to drive the ECM such that the actual motion of the agitator closely approximates the command motion of the agitator based on the user""s selection of a particular agitator cycle. Additionally, the actual current flowing to the ECM is monitored to ensure that it remains within predetermined upper and lower current limits relative to the current command.